I don't understand QoT QQ aggro, but if Sedna throws out a 1500 (if i remember her last rank value correctly) point heal nobody seems to care. I think the difference between the two is that a heal still allows the attacker to see their big numbers, whereas the bramble shield only shows absorbed, therefore deflating epeens. When the epeen is not happy the player is not happy.
There is actually some marginal difference, heal has greater cast time afaik and shield is rather passive after used if you know what I mean. And if you are at full hp heal won't do you any good, on the contrary shield will temporaryli extend your hp.